Individuals may experience different warning signs and sometimes there may be no obvious warning. Some commonly experienced signs include:
• Frequent urination
• Increased thirst
• Extreme tiredness or lack of energy
• Constant hunger
• Recurrent infections
• Blurred vision
• Vomiting and stomach pain
• Tingling session in feet or hands
• Lack of interest or concentration
• Frequent infections
• Slow-healing wounds

Type 1 diabetes: onset is usually sudden and dramatic.

Type 2 diabetes:
Symptoms can often be mild or absent, making this type of diabetes gradual in onset and hard to detect. 
Many people with Type 2 diabetes remain unaware of the illness until complications of diabetes have developed when parts of the body have been damaged by excess blood glucose.

Reference: www.idf.org/warning-signs-diabetes